1. Field of the Invention
The present invention relates to a solid-state imaging apparatus and an imaging system.
2. Description of the Related Art
In a solid-state imaging apparatus, charges generated by a photoelectric converter are converted into a voltage by a charge-voltage converter such as a floating diffusion. Let Q be the charges, V be the voltage, and C be the capacity of the charge-voltage converter. Since V=Q/C, the sensitivity can be improved by reducing the capacity of the charge-voltage converter.
Japanese Patent Laid-Open No. 7-58308 discloses a solid-state imaging apparatus including a light receiving unit 1, a storage unit 2, a horizontal transfer unit 3, a floating diffusion 23, an output amplifier 27, and a buffer amplifier 31. The light receiving unit 1 includes a plurality of shift registers that are continuous in the vertical direction. The storage unit 2 includes a plurality of shift registers following those of the light receiving unit 1 and stores information charges corresponding to one screen. The horizontal transfer unit 3 receives, for each horizontal line, the information charges of one screen stored in the storage unit 2 and outputs them sequentially. The floating diffusion 23 temporarily stores the information charges output from the horizontal transfer unit 3. The floating diffusion 23 is connected to the input terminal of the output amplifier 27 via an aluminum wiring 26. The output amplifier 27 is formed from a two-stage source follower circuit. The output terminal of the output amplifier 27 is connected to the input terminal of the buffer amplifier 31. The signal output from the buffer amplifier 31 has the same phase as that of the potential variation that occurs in the floating diffusion 23, and is applied to an aluminum wiring 30 serving as a light shielding film that covers the floating diffusion 23. Hence, even when the aluminum wirings 26 and 30 oppose on both sides of an insulating film 29, the actual capacity between them is sufficiently small so as to suppress the increase in the capacity of the floating diffusion 23.
However, the invention described in Japanese Patent Laid-Open No. 7-58308 only aims at the final output portion of a CCD solid-state image sensor without considering the capacity of the charge-voltage converter of each pixel in a pixel array. Additionally, in the related-art invention, the output signal of the buffer amplifier is merely applied to the aluminum wiring to suppress the increase in the capacity of the floating diffusion caused by the aluminum wiring serving as a light shielding film that shields the floating diffusion from light. That is, in the related-art invention, the output signal of the buffer amplifier is not applied to the aluminum wiring arranged between an electrical conductor and the charge-voltage converter to suppress the increase in the capacity of the charge-voltage converter caused by the electrical conductor maintained at a fixed electric potential.